Hydroxylation activated drug release

ABSTRACT

The present invention concerns prodrugs whose aromatic oxidation, particularly their enzymatic aromatic hydroxylation, results in their activation by the release of a drug moiety. It particularly concerns anti-tumour prodrugs and those which are specifically activated by the hydroxylation activity of the P-450 enzyme CYP1B1.

[0001] The present invention concerns prodrugs whose aromatic oxidation, particularly their enzymatic aromatic hydroxylation, results in their activation by the release of a drug moiety. It particularly concerns anti-tumour prodrugs and those which are specifically activated by the hydroxylation activity of the P-450 enzyme CYP1B1.

[0002] Many conventional cytotoxic drags are known (for example colchicine, esperimycin, taxol, daunomycin and staurosporin) which can be used for chemotherapeutic purposes. However, they typically suffer from the problem that they are generally cytotoxic and therefore may affect cells other than those which it is wished to target. This can be alleviated somewhat by using targetted drug delivery systems, for example direct injection to a site of tumourous tissue, or by e.g. binding the cytotoxic agent to antibody which specifically recognises an antigen displayed by cancerous cells. Alternatively, electromagnetic radiation may be used to cause chemical changes in an agent at a desired site in the body such that it becomes cytotoxic. However, all of these techniques have, to a greater or lesser extent, certain limitations and disadvantages.

[0003] It has been reported (Murray, G. I. et al., 15 Jul. 1997, Cancer Research, 57: 3026-3031) that the enzyme CYP1B1, a member of the cytochrome P450 family of xenobiotic metabolizing enzymes, is expressed at a high frequency in a range of human cancers including cancers of the breast, colon, lung, oesophagas, skin, lymph node, brain and testis, and that it is not detectable in normal tissues. This led to the conclusion (p. 3030, final sentence) that “. . . the expression of CYP1B1 in tumour cells provides a molecular target for the development of new anticancer drugs that could be selectively activated by the presence of CYP1B1 in tumour cells”. It was also reported (p.3030, column 1 lines 15-17) that CYP1B1 is capable of 4-hydroxylation of estradiol. No specific anticancer drugs were suggested.

[0004] The present inventors have now succeeded in creating a range of prodrugs having a “carrier” framework with a drug moiety conjugated to it (the prodrug other than the drug moiety is referred to below as “the rest of the prodrug”) which have little or no cytotoxic effect when in their normal state, but whose aromatic oxidation e.g. hydroxylation (for example by CYP1B1) results in the release of the drug moiety. With CYP1B1 as a hydroxylating enzyme, this provides for a self-targetting drug delivery system in which a non-cytotoxic (or at least negligibly cytotoxic) compound can be administered to a patient, for example in a systemic manner, the compound then being hydroxylated at the site of tumour cells (intratumoural hydroxylation) to release the drug which acts to kill or otherwise affect the tumour cells. The fact that CYP1B1 is not expressed by normal cells means that the hydroxylation of the prodrug only occurs at the site of tumour cells and therefore only tumour cells are affected, thus providing a self-targetting drug delivery system.

[0005] The prodrugs of the present invention have the distinct advantage of being useful in the treatment of tumours at any site in the body, meaning that even tumours which have undergone metastasis (which are not normally susceptible to site-specific therapies) may be treated, as well of course as primary and secondary tumours.

[0006] The prodrugs may be designed to be activated by other oxidising agents, for example other enzymes (e.g. other members of the cytochrome P-450 family of enzymes) which cause hydroxylation of the prodrug.

[0007] CYP1B1 has not yet been fully characterised, and it is therefore possible that tumour-specific isoforms of it may exist which possess the same catalytic properties. The prodrugs of the present invention may, of course, be used with such enzymes.

[0008] In the case of cytochrome P-450 activated prodrugs, the therapeutic strategy achieved using them is referred to as SPEAR (Specific P-450 Enzyme Activated drug Release).

[0009] According to the present invention there is provided a prodrug comprising a drug moiety bound to a carrier framework, the prodrug being activated by aromatic oxidation of the carrier framework to release the drug moiety.

[0010] The prodrug may be activated by aromatic hydroxylation. It may be activated by enzymatic aromatic hydroxylation.

[0011] Other enzymatically-activated prodrugs are known, for example those which release a drug moiety as the result of cleavage by a peptidase enzyme. However, nowhere has it been previously suggested that a prodrug could be activated to release a drug moiety by enzymatic hydroxylation.

[0012] A prodrug according to the present invention may have the formula (Z):

[0013] wherein:

[0014] X=H, OH, OMe or N(CH₃)₂; and

[0015] n=0-6;

[0016] and:

[0017] R₁=H, C₁₋₄ lower alkyl, or together with R₂ forms part of a cycloalkyl group which may be further substituted to form part of a polycyclic cycloalkyl group, or with R₂ forms part of a steroidal carbon framework;

[0018] R₂=H, C₁₋₄ lower alkyl, or together with R₁ and/or R₃ forms part of a cycloalkyl, polycyclic cycloalkyl or steroidal carbon framework, or forms part of a polycyclic aromatic group by linkage to R₄;

[0019] R₃=H, C₁₋₄ lower alkyl or together with R₂ forms part of a cycloalkyl, polycyclic cycloalkyl or steroidal carbon rework; and

[0020] R₄=H or is fused directly to the aromatic position designated by R₂ and either:

[0021] the drug moiety is derived from a drug having a free amino, hydroxyl or thiol group and which links it to the rest of the prodrug, such that A represents NH, NR (R=C₁₋₄ lower alkyl), O or S; or

[0022] the drug moiety is derived from a drug having a carboxylate group, an ester linkage joining it to the rest of the prodrug and A being absent.

[0023] Enzymatic hydroxylation of the prodrugs of formula (Z) results in the transfer of electrons from the site of hydroxylation (for example the aromatic 4 position—see FIG. 1) to the drug moiety, resulting in its release.

[0024] The prodrug may, for example, be an anti-tumour prodrug. The drug moiety may be cytotoxic or cytostatic, although of course it may be a moiety which has any other desired effect. Examples of classes of drug moiety include antimitotic agents, alkylating agents, antifolates, DNA-damaging agents and enzyme inhibitors. Specific examples of possible cytotoxic drug moieties include colchicine, esperimycin, taxol, daunomycin, staurosporin, and nitrogen mustard. Alternatively, the drug moiety could be e.g. a fluorescent organic molecule which would be released in an intratumoural manner, aiding tumour detection by correlating specific cell fluorescence with the presence of the drug moiety and thus of the oxidising agent (e.g. CYP1B1) which caused its release.

[0025] Thus the term “drug” also extends to moieties which may be used for diagnostic purposes.

[0026] A possible nitrogen mustard is, for example, a para-hydroxy aniline mustard that is linked through the para-hydroxy group to the rest of the prodrug. In the case of nitrogen mustard prodrugs, the mustard function is itself activated only when the drag moiety is released from the prodrug.

[0027] The olefin linkage

[0028] may have a cis- or trans-geometry. It may be acyclic or cyclic. It may form part of an aromatic or polycyclic aromatic system.

[0029] The prodrug may be activated by CYP1B1. Thus a prodrug which releases a cytotoxic drug moiety upon hydroxylation by CYP1B1 may be used as a self-targetting anti-tumour drug, being activated at the site of a tumour by CYP1B1and having no (or negligible) cytotoxicity in the rest of the body.

[0030] The linkage to the drug moiety from the carrier framework may be from a hydroxyalkyl group in the prodrug via a carbamate, carbonate or thiocarbonate linker to an amino, hydroxy or thiol group in the drug moiety.

[0031] Using the strategy and prodrugs of the present invention, it is possible to link any desired drug moiety through a free amino, hydroxy or thiol group. The provision of a linker group comprising a carbamate, carbonate or thiocarbonate linker joining the drug moiety to the rest of the prodrug results in the release of carbon dioxide upon release of the drug moiety, making the reaction irreversible. Thus the hydroxylation (or other aromatic oxidation) of the prodrug may cause the release of the drug moiety and carbon dioxide.

[0032] A prodrug may have a steroid carbon carrier framework. For example, it may be derived from estradiol.

[0033] An example of a prodrug according to the present invention is the prodrug having the formula I, shown in FIG. 1. It is an estradiol derivative and incorporates the drug moiety at the steroid 6-position. In this position, the 3-hydroxy group of estradiol does not provide the requisite electron release, but upon 4-hydroxylation the electron release from the 4-hydroxy group triggers electron transfer within the prodrug, resulting in the release of the drug moiety.

[0034] A prodrug according to the present invention may, for example, have the formula of any one of formulae (I)-(IX):

[0035] wherein —OR=—OMe or —OH

[0036] The prodrug may have the formula of any one of formulae (X)-(XV):

[0037] Formula (X) is a colchicine-estradiol prodrug; (XI) is a combretastatin-estradiol prodrug; (XII) is a mustard-estradiol prodrug; (XIII) is a fluorophore-estradiol conjugate; (XIV) is a colchicine-naphthyl prodrug; and (XV) is a colchicine-benzyl prodrug.

[0038] Also provided according to the present invention is a prodrug according to the present invention for use in a method of treatment or diagnosis of the human or animal body, particularly the treatment or diagnosis of tumours.

[0039] Also provided according to the present invention is the use of a prodrug according to the present invention in the manufacture of a medicament, e.g. for the treatment of tumours.

[0040] Also provided according to the present invention is a method of manufacture of a medicament, comprising the use of a prodrug according to the present invention.

[0041] Also provided according to the present invention is a method of treatment of a patient, comprising administering to the patient a prodrug according to the present invention. The prodrug may be administered to treat a medical condition e.g. an illness.

[0042] Methods of manufacture of medicaments are well known. For example a medicament may additionally comprise a pharmaceutically acceptable carrier, diluent or excipient (Remington's Pharmaceutical Sciences and US Pharmacopeia, 1984, Mack Publishing Company, Easton, Pa., USA)

[0043] The exact dose (i.e. a pharmaceutically acceptable dose) of prodrug to be administered to a patient may be readily determined by one skilled in the art, for example by the use of simple dose-response experiments.

[0044] Since prodrugs of the present invention may be specific to e.g. tumour cells, they may not only be used to treat tumours, but may also be used to determine whether or not a patient (or a sample taken from a patient) has tumour cells. For example, tumour cells may be detected by using a SPEAR prodrug that is a fluorophore conjugate which releases a fluorescent compound upon enzymatic hydroxylation. An example of this type of fluorophore conjugate is given by compound (XIII) below. Cell numbers in a sample may be assayed, as may the presence and quantity of the oxidised e.g. hydroxylated prodrug, thus providing for the diagnosis of the presence of tumour cells.

[0045] The invention will be flier apparent from the following description, with reference to the several figures of the accompanying drawings, which show, by way of example only, forms of prodrug.

[0046] Of the figures:

[0047]FIG. 1 shows the estradiol-derived prodrug having the formula (I), together with its 4-hydroxylation; and

[0048]FIG. 2 shows the synthesis of an estradiol-colchicine prodrug. R is designated as representing H or a protecting group, for example an acetate group (COCH₃) or a benzyl group (CH₂C₆H₅).

[0049] The synthesis of the estradiol-colchicine prodrug I is shown in FIG. 2. The synthetic route uses estradiol as a starting material. The 6-oxo group is introduced by oxidation of estradiol with pyridinium chlorochromate to give 6-oxo estradiol. This is then subjected to borohydride reduction to produce 6-hydroxy estradiol. The desired cytotoxic agent is then coupled to the 6-hydroxy estradiol using triphosgene as coupling agent (Eckert and Foster, 1987, Angew. Chem. Int. Ed Engl., 26: 894-895) to provide the carbamate linked estradiol prodrug. In the synthesis of the prodrug, the R group is initially a protecting group (for example an acetate group). Once the final step (above) has been taken, the protecting groups are substituted with hydrogen to give the final prodrug product. The chemistry of protecting groups and their substitution is well known and will be readily apparent to one skilled in the art.

[0050] 4-hydroxylation of the prodrug (FIG. 1) results in electron transfer from the 4-hydroxy group, causing release of the drug moiety and carbon dioxide. The release of carbon dioxide makes the reaction irreversible.

[0051] The invention is exemplified by the specific SPEAR prodrugs given in the formulae (X) to (XV). Compound (X) is a carbamate linked colchicine-estradiol prodrug, which releases the cytotoxic agent des-acetyl colchicine upon enzymatic hydroxylation by CYP1B1. Compound (XI) is a carbonate linked combretastatin-estradiol prodrug. Compound (XII) is a SPEAR prodrug of a nitrogen mustard, which generates the highly cytotoxic alkylating agent, bis(chloroethyl)amine mustard, upon enzymatic hydroxylation. Compound (XIII) is a SPEAR fluorophore conjugate which releases the fluorescent compound 7-amino4-methylcoumarin upon enzymatic hydroxylation. Compound (XIV) is an example of a non-steroidal SPEAR prodrug of colchicine linked to 6-methoxy-1-naphthalenemethanol. Compound (XV) is an example of a non-steroidal SPEAR prodrug derived from 3-methoxybenzyl alcohol.

[0052] Prodrug Metabolism Studies

[0053] A microsomal preparation of resected human tumour tissue expressing the cytochrome P-450 CYP1B1 enzyme was prepared essentially as described by the method of Barrie et al. (1989, J. Steroid Biochem., 6: 1191-1195). The prodrug metabolism experiment was carried out under yellow light, at 37° C.

[0054] An array of 1.5 ml centrifuge tubes were set up in a water bath shaker under aerobic conditions. To each tube was added 500 μl of pH 7.6 buffer (0.1 M NaK₂PO₄), followed by an aqueous solution of NADPH (5 μl of a 25 mM stock solution). The microsomal preparation (80 μl) was then added and the tubes preincubated for 5 minutes at 37° C. The prodrug substrate was then added (10 μl of a 5 mM stock solution) and incubated for 1 hour at 37° C. After 1 hour the tubes were transferred to an ice/water cooling bath (0° C.). The tubes were then centrifuged at 15,000 rpm for 30 minutes. A sample of the supernatant (100 μl) was then taken and analysed by HPLC, using the following BPLC conditions: Spherisorb C18 (25 cm×4.6 mm id), used without guard column. Flow rate 1 ml/min. Eluent 75% 0.1 M. KH2PO4 and 25% acetonitrile. Metabolism of the prodrugs in this way was found to result in release of the free drug moiety. For example, tumour microsomal metabolism of the colchicine-estradiol prodrug compound (X) liberated free N-desacetyl colchicine, which was detected by HPLC analysis.

[0055] Prodrug Synthesis

[0056] Estradiol 3,17-dipivaloate

[0057] Pivaloyl chloride (664 mg; 5.5 mmol) was added dropwise to a solution of estradiol (250 mg; 0.9 mmol) in 1:1 pyridine/dichloromethane (3 ml) at 0° C. After 15 hours the reaction was quenched with water (10 ml) and the product was extracted with ether (3×10 ml). The combined organic layers were washed sequentially with 10% HCl (15 ml), saturated aqueous copper sulfate (15 ml) and brine (15 ml), dried over MgSO₄ and finally concentrated in vacuo. The residue was recrystallised from hot ethanol and isolated as a white crystalline solid (247 mg; 61%). IR(cm⁻¹, KBr): (3000, CH) (1700, COO) (1500, ArC═C) (1300, CH3); 1H-NM (250 MHz, CDCl3): (H (0.9, s; 3H) (1.2, s; 9H) (1.3, s; 9H) (1.4, m; 6H) (1.8, m; 3H) (2.3, m; 3H) (2.9, t; 2H) (4.7, t; 1H) (6.8, m; 2H) (7.1, d; 1H); 13C-NMR (250 MHz, CDCl3): (c 12.0, 23.3, 26.1, 27.0, 27.1, 27.2, 27.6, 29.5, 36.9, 38.2, 38.8, 39.9, 43.1, 43.9, 49.8, 82.2, 118.4, 121.3, 126.3, 137.5, 138.0, 148.9, 157.8, 177.3, 178.5; Mass Spectrum (M+1) m/e=441.

[0058] 6-Oxoestradiol 3,17-dipivaloate

[0059] 3, 5-Dimethylpyrazole (545 mg; 5.7 mmol) was added to a suspension of chromium trioxide (576 mg; 5.7 mmol) at −20° C. in dichloromethane (2 ml). After stirring for 15 minutes, estradiol 3,17-dipivaloate (250 mg; 0.57 mmol) in dichloromethane (1 ml) was added dropwise and the reaction mixture was stirred at −15° C. for 4 hours. The reaction was quenched with water (15 ml) and the aqueous layer was extracted with ether (3×15 ml). The combined organic layers were washed with water (15 ml) and brine (15 ml), dried over MgSO₄ and concentrated in vacuo. The residue was chromatographed on silica gel and the product was isolated as a white solid (55 mg; 21%). IR (cm⁻¹, KBr): (3000, CH) (1700, COO) (1650, ArCO) (1500, ArC═C) (1300, CH3); 1H NMR (CDCl3): (H(0.9, s; 3H) (1.2, s; 9H) (1.39, d; 9H) (1.41, m; ,6H) (1.9, m; 2H) (2.2, m; 2H) (2.3, m; 1H) (2.4, m 1H) (2.7, d; 1in) (4.7, t; 1H) (7.2, d; 1H) (7.4, d; 1H) (7.6, d; 1H); 13C NMR (CDCl3): (c 11.9, 22.9, 25.3, 27.1, 27.2, 27.4, 36.5, 38.9, 39.1, 39.5, 42.9, 43.0, 43.8, 49.8, 81.7, 119.9, 126.6, 126.9, 133.6, 144.0, 149.8, 178.4, 196.9; Mass Spectrum (M+1) m/e=455.

[0060] 6-Hydroxyestradiol 3,17-dipivaloate

[0061] Sodium borohydride (104 mg; 2.8 mmol) was added to 6-oxoestradiol 3,17-dipivaloate (500 mg; 1.1 mmol) in ethanol (20 ml) at 25° C. under nitrogen. The reaction was quenched with water (100 ml) after 48 hours, and the aqueous layer was extracted with dichloromethane (3×50 ml). The organic layers were combined, dried over MgSO₄ and concentrated in vacuo. The product was purified on silica gel and isolated as an off-white solid (150 mg; 30%). Mass Spectrum (M+1) m/e=457.

[0062] Compound (X): Colchicine-Estradiol Prodrug

[0063] To a solution of triphosgene (0.25 mmol, 74 mg) in dichloromethane (1 ml) was added a solution of 6-hydroxyestradiol 3,17-dipivaloate (0.3 mmol, 137 mg) and diisopropylamine (0.6 mmol, 0.1 ml) in dichloromethane (1.5 ml). The mixture was stirred for 30 minutes, then a solution of N-desacetyl colchicine (0.3 mmol, 107 mg) and diisopropylamine (0.6 mmol, 0.1 ml) in dichloromethane (1.5 ml) was added and the mixture stirred for 1 hour. The reaction mixture was then evaporated to dryness, the residue redissolved in ethyl acetate, and washed with 0.5 M NaCO₃ (aq). The ethylacetate solution was then dried over MgSO₄, and concentrated in vacuo to finish the title prodrug as its 3,17-dipivaloate ester.

[0064] The prodrug dipivaloate ester was then dissolved in methanol (3 ml) and an aqueous solution of methylamine (40% w/w, 0.5 ml) added, and the solution stirred for 1 hour. Dilute HCl (0.1 M) was then added to neutralise the mixture to pH 7, and the product then extracted with dichloromethane (3×10 ml). The solvent was then evaporated in vacuo to give the title colchicine-estradiol prodrug. IR (KBr) 1695 cm−1; MS (M+1) m/e=672.

[0065] Compound (XI): Combretastatin-Estradiol Prodrug

[0066] The procedure followed that described for compound (X) above, but using combretastatin (0.3 mmol, 95 mg) in place of N-desacetyl colchicine, to afford the title combretastatin prodrug. IR (KBr) 1750 cm−1; MS (M+1) m/e=631.

[0067] Compound (XII): Mustard-Estradiol Prodrug

[0068] The procedure followed that described for compound (X), but using bis(chloroethyl)amine hydrochloride (0.3 mmol, 53 mg) in place of N-desacetyl colchicine together with an extra equivalent of diisopropylamine (0.6 mmol, 0.1 ml). This gave the title mustard prodrug as a white crystalline compound. IR (KBr) 1700 cm−1; MS (M+1) m/e=456.

[0069] Compound (XIII): Fluorophore-Estradiol Conjugate

[0070] The procedure followed that described for compound (X) but using 7-amino-4-methylcoumarin (0.3 mmol, 53 mg) in place of N-desacetyl colchicine, to afford the title fluorophore conjugate. IR (KBr) 1690 cm−1; MS (M+1) m/e=490.

[0071] Compound (XIV): Colchicine-Naphthyl Prodrug

[0072] To a solution of triphosgene (0.25 mmol, 74 mg) in dichloromethane (1 ml) was added a solution of 6-methoxy-1-naphthalenemethanol (0.3 mmol, 56 mg) and diisopropylamine (0.6 mmol, 0.1 ml) in dichloromethane (1.5 ml). The mixture was stirred for 30 minutes, then a solution of N-desacetyl colchicine (0.3 mmol, 107 mg) and diisopropylamine (0.6 mmol, 0.1 ml) in dichloromethane (1.5 ml) was added and the mixture stirred for 1 hour. The reaction mixture was then evaporated to dryness, the residue redissolved in ethylacetate, and washed with 0.5 M NaCO₃ (aq). The ethylacetate solution was then dried cover MgSO₄, and concentrated in vacuo to finish the title colchicine-naphthyl prodrug. IR (KBr) 1695 cm−1; MS (M+1) m/e=572.

[0073] Compound (XV): Colchicine-Benzyl Prodrug

[0074] To a solution of triphosgene (0.25 mmol, 74 mg) in dichloromethane (1 ml) was added a solution of 3-methoxybenzyl alcohol (0.3 mmol, 41 mg) and diisopropylamine (0.6 mmol, 0.1 ml) in dichloromethane (1.5 ml). The mixture was stirred for 30 minutes, then a solution of N-desacetyl colchicine (0.3 mmol, 107 mg) and diisopropylamine (0.6 mmol, 0.1 ml) in dichloromethane (1.5 ml) was added and the mixture stirred for 1 hour. The reaction mixture was then evaporated to dryness, the residue redissolved in ethylacetate, and washed with 0.5 M NaCO₃ (aq). The ethylacetate solution was then dried over MgSO₄, and concentrated in vacuo to finish the title colchicine-benzyl prodrug. IR (KBr) 1695 cm−1; MS (M+1) m/e=522. 

1. A prodrug comprising a drug moiety bound to a carrier framework, the prodrug being activated by aromatic oxidation of the carrier framework to release the drug moiety.
 2. A prodrug according to claim 1, being activated by aromatic hydroxylation.
 3. A prodrug according to claim 2, being activated by enzymatic aromatic hydroxylation.
 4. A prodrug according to claim 1, and having the formula (Z):

wherein: X=H, OH, OMe or N(CH₃)₂; and n=0-6; and: R₁=H, C₁₋₄ lower alkyl, or together with R₂ forms part of a cycloalkyl group which may be further substituted to form part of a polycyclic cycloalkyl group, or with R₂ forms part of a steroidal carbon framework; R₂=H, C₁₋₄ lower alkyl, or together with R₁ and/or R₃ forms part of a cycloalkyl, polycyclic cycloalkyl or steroidal carbon framework, or forms part of a polycyclic aromatic group by linkage to R₄; R₃=H, C₁₋₄ lower alkyl or together wit R₂ forms part of a cycloalkyl, polycyclic cycloalkyl or steroidal carbon framework; and R₄=H or is fused directly to the aromatic position designated by R₂ and either: the drug moiety is derived from a drug having a free amino, hydroxyl or thiol group and which links it to the rest of the prodrug, such tat A represents NH, NR (R=C₁₋₄ lower alkyl), O or S; or the drug moiety is derived from a drug having a carboxylate group, an ester linkage joining it to the rest of the prodrug and A being absent
 5. A prodrug according to claim 1, being an anti-tumour prodrug.
 6. A prodrug according to claim 1, the drug moiety being a cytotoxic or cytostatic agent.
 7. A prodrug according to claim 6, a cytotoxic drug moiety being selected from the group of colchicine, esperimycin, taxol, daunomycin, staurosporin, and nitrogen mustard.
 8. A prodrug according to claim 1, being activated by hydroxylation by CYP1B1.
 9. A prodrug according to claim 1, the drug moiety being an antimitotic agent, an alkylating agent, an antifolate, a DNA damaging agent or an enzyme inhibitor.
 10. A prodrug according to claim 4, the olefin linkage

having a cis- or trans-geometry.
 11. A prodrug according to claim 4, the olefin linkage

being acyclic or cyclic.
 12. A prodrug according to claim 4, the olefin linkage

forming part of an aromatic or polycyclic aromatic system.
 13. A prodrug according to claim 1, the linkage to the drug moiety from the carrier framework being from a hydroxyalkyl group in the prodrug via a carbamate, carbonate or thiocarbonate linker to an amino, hydroxy or thiol group in the drug moiety.
 14. A prodrug according to claim 1, having a steroid carbon carrier framework.
 15. A prodrug according to claim 1, being derived from estradiol.
 16. A prodrug according to claim 4, having the formula of any one of formulae (I)-(IX):

wherein —OR=—OMe or —OH.
 17. A prodrug according to claim 4 having the formula of any one of Formulae (X)-(XV):


18. A prodrug according to any one of the preceding claims, its aromatic oxidation being by hydroxylation and causing the release of the drug moiety and carbon dioxide.
 19. A prodrug according to claim 1 for use in a method of treatment or diagnosis of the human or animal body.
 20. The use of a prodrug according to claim 1 in the manufacture of a medicament.
 21. A method of manufacture of a medicament, comprising the use of a prodrug according to claim
 1. 22. A method of treatment of a patient, comprising administering to the patient a prodrug according to claim
 1. 